There has developed in the polymer field, and especially in the packaging and related industries, a need for thermoplastic polymers that can be formed into colorless, transparent articles having good impact strength and ductility. There are needs for polymers which are useful as single components as well as for use in blends with other commonly used polymers to make articles with improved properties. The polymers satisfying these needs should be suitable for use with conventional extrusion, injection and blow molding equipment and also suitable for use in other methods of forming plastics into containers, tubes, films, fibers, and the like. Polystyrene, high impact polystyrene, branched block copolymers, and the like have been developed to meet these criteria with various degrees of satisfaction.
Much effort has been directed to the preparation of substantially transparent block copolymer resins with a variety of block structures produced by a variety of monomer addition sequences and a variety of coupling agents. Desirable properties and an economic advantage can be obtained by blending some monovinylaromatic-conjugated diene copolymers with polystryene polymers. However, because blueness of blends of monovinylaromatic-conjugated diene copolymers with polystyrene polymers cannot be predicted by rule of mixtures behaviors, getting a desirable combination of properties can be a complicated task. Sometimes relatively colorless monovinylaromatic-conjugated diene copolymers give blends with high blueness when blended with colorless general purpose polystyrene.
Blueness of articles formed from various copolymers and blends of copolymers with other polymers is a longstanding problem in applications where colorless materials which also have good impact strength and ductility are desirable. Specific examples include materials for water and food containers.